Modern aircraft are often powered by a propulsion system that includes a gas turbine engine housed within an aerodynamically streamlined nacelle. A fan section of the gas turbine engine includes a fan assembly and a fan casing. The fan assembly includes a fan rotor hub centered on and rotatable about an axially extending centerline of the engine, and a plurality of fan blades that are attached to and extend radially out from the fan rotor hub. The fan casing is disposed radially outside of and circumferentially around the fan assembly. The high-energy impact of a broken fan blade (commonly referred to as “blade out”) (the broken fan blade hereinafter referred to as a “released fan blade” or simply a “released blade”) on an operating gas turbine engine can be undesirable. A released fan blade is released from the rotating fan assembly when broken. If the released fan blade is not isolated from the rotating fan assembly, the released fan blade can interfere with the remaining blades during their deceleration. A fan containment case for the fan casing captures the released blade, preventing the released blade from penetrating the engine housing while providing a space for the released blade outside of the rotation path of the remaining blades.
Fan containment cases must be as lightweight as possible for aircraft operating efficiency, yet provide the critical level of protection against the released fan blade, taking into account all the requirements, including space limitations, of the engine nacelle. Conventional fan containment cases may include a stiff but crushable material and a containment covering comprising a lightweight and high strength ballistic material wrapped in multiple layers around the crushable material. There may be additional layers in the conventional fan containment case. During normal operation, the crushable material provides stiffness to the fan containment case. When a fan blade breaks in flight, the released blade penetrates the fan containment case and strikes the crushable material. The crushable material deflects radially and crushes under the immense centrifugal force of the released blade to provide a blade capture pocket for capturing the released blade, thereby isolating the released blade from the rotating fan assembly.
The containment covering of the conventional fan containment case resists penetration by the released blade and confines the released blade to a predetermined circumferential envelope in the engine nacelle. When the released blade impacts the containment covering, because of the high friction between the continuous fabric layers making up the containment covering and the edge constraints thereof, the released blade stretches the containment covering in a local region, resulting in local deformation and damage at the impact location. Therefore, while a released blade is likely to be contained by the containment covering, the individual fibers of the containment covering may be pushed aside by the released blade, creating a small local opening at the impact location through which released blade fragments may unacceptably escape. Therefore, tighter and thus heavier braided ballistic material and/or many more continuous layers of ballistic material than necessary are used for the containment covering in the conventional fan containment case to ensure critical containment of the released blade and released blade fragments within the circumferential envelope and engine nacelle. Such over engineering results in excess material usage, weight, as well as cost inefficiencies. For example, a conventional containment covering of Kevlar® ballistic material may undesirably account for 25% or more of the weight of the fan containment case for engines in which it is used.
Accordingly, it is desirable to provide fan containment cases for fan casings in gas turbine engines, fan blade containment systems, and methods for producing the same. In addition, it is desirable to enable the use of less and/or lighter weight ballistic material for the containment covering, thereby reducing the weight and cost of the containment covering and fan containment case for increased aircraft operating efficiency. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.